Extreme forms of inequality achieved by huge jumps in income for the world's highest-paid are becoming a serious macroeconomic issue, author Thomas Piketty told CNBC on Tuesday.
"There's no problem with inequality per se. The problem is when inequality gets too extreme and if the top is rising three times faster than the average, you can see that this cannot continue forever," Piketty said.
"At some point this will have to stop and we should try to have more transparency about income and wealth."
A recent AP/Equilar study found that chief executives now make about 257 times the average worker's salary, up sharply from 181 times in 2009.
Progressive taxation could go some way to achieve greater equality but while tackling the issue was an issue for big economies, Piketty conceded that it has been more of a challenge for smaller countries.
"Are we going to solve that alone as individual European countries? No. We need international agreement," he said.